Oscar Pistorius' defense appeared to have suffered a blow today when a forensic witness who contradicted the prosecution's version of the shooting of Reeva Steenkamp was challenged on his credentials as an expert in forensics and other elements of his testimony.

The witness, Roger Dixon, was forced to admit under questioning by prosecutor Gerrie Nel that he was not an expert in forensics, pathology, ballistics, blood spatter, or sound and optics.

Dixon told the court Tuesday that Steenkamp was close to the door and angling toward the door on her right side as if she was reaching for the doorknob. He also concluded that Pistorius fired four shots through the bathroom door in quick succession.

Dixon's testimony contradicts the prosecution's forensic experts who determined that Steenkamp was facing the door when the first bullet struck her in the hip and knocked her down. Nel had also told the court that she was afraid of Pistorius and was talking to him through the locked door when he shot her.

The prosecution had also argued that Pistorius fired one shot and Steenkamp screamed before Pistorius fired three more rounds.

Pistorius, 27, is charged with murder for shooting Steenkamp, 29, before dawn on Valentine's Day 2013. He could be sentenced to at least 25 years if convicted. Pistorius, a legless paralympian sprinter known as Blade Runner, claims he mistook Steenkamp for an intruder.

Dixon's testimony included a bullet-by-bullet account of Steenkamp's wounds, prompting another bout of retching by Pistorius in court.

In addition to giving a different version of how Steenkamp was shot, Dixon told the court that he helped record sounds of a cricket bat hitting against a door to show to the court that the sounds neighbors testified were the sound of gunshots could have been Pistorius breaking down the door to get to his mortally wounded girlfriend.

Nel questioned Dixon's expertise and professional affiliations.

"Are you a sound expert?" Nel asked.

"I would hope I'm a sound expert," he replied.

Nel repeated the question, referring to sound and acoustics specifically, to which Dixon said the test he did of the sound made by a cricket bat hitting a door and a gun firing was to determine whether the two could be confused.

"[The] expertise used was attempting to reconstruct the situation... I was not listening to myself making that sound," he said.

Nel asked Dixon how he conducted tests on how dark it would have been in Pistorius' bedroom when he claims he didn't know Steenkamp had gone into the bathroom.

"The instruments that I used were my eyes," Dixon said.

Dixon's qualifications as a forensics expert were also questioned by Nel, with the prosecutor getting so aggressive that the judge admonished him, "Mr. Nel, please restrain yourself.”